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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a floating-type composite magnetic head and the
production method thereof, more particularly, to a magnetic head wherein
the magnetic gap depth is precisely controlled by inserting and molding a
magnetic core provided with concave marks on its side surface into a slit
provided in a slider.
2. Related Art
FIG. 4 shows an example of a magnetic core being used in a floating-type
composite magnetic head. The magnetic core 41 comprises a C-shaped core 42
and an I-shaped core 43 joined together and bonded over a gap spacer so
that a magnetic gap 44 is formed between them. The C-shaped core 42 and
I-shaped core 43 are usually made of such materials as, for example,
single crystal ferrite and, recently, in order to meet increasing
requirements for high density storage, it is usual to apply a
high-permeability magnetic film such as Fe--Al--Si alloy film on the
surfaces facing the magnetic gap of either one or both of the cores.
With the example as per FIG. 4, said high permeability magnetic films 45
and 46 are applied to both the C-shaped core and I-shaped core. In FIG. 4,
numeral 47 represents the depth of the magnetic gap 44, or the distance
between the magnetic core surface facing the storage medium and the apex
(the point on the C-shaped core where the plane forming the magnetic gap
intersects with the inclined plane, whereby the gap distance by the plane,
formed between the C-shaped and I-shaped cores remains the same and
whereby the gap distance by the inclined plane gradually increases, and
the point is indicated by a point or line in the drawing). The dimensional
preciseness of the depth of the magnetic gap has a significant influence
on the reading and reproducing characteristics.
Consequently, strict control of the apex position is very important in the
production of these magnetic heads. Meanwhile, numeral 48 stands for
reinforcing glass which fills the space between the C-shaped core 42 and
I-shaped core 43 to firmly join the cores together, the filler extending
all the way to the end of the coil winding clearance 49.
FIG. 5 is a schematic diagram showing an example of the structure of a
floating-type composite magnetic head. The slider 52 of this floating-type
composite magnetic head 51 is equipped with air bearings 53a and 53b to
float on the magnetic disc (omitted from the drawing) functioning as the
magnetic storage medium at both ends of its plane which faces the magnetic
disc, air bearing 53a of the air bearings being equipped with a slit 54.
The slit 54 is usually provided on the trailing side off the storage
medium (which can be referred to as the air outlet side). A magnetic core
55 is inserted into the slit 54 and molded using glass filler 56. Numeral
57 represents a slot which is formed so that the coil winding clearance 58
maintained after molding the magnetic core 55.
A floating-type composite magnetic head of the structure is being produced
under, for example, the method given below. FIG. 6 is an elevation of a
floating-type composite magnetic head viewed from the slotted end. The
exemplified production method includes inserting the magnetic core 61 into
the slit 64 and placing a glass rod over the air-bearing side of the slit
before heating the glass rod to melt it under a vacuum atmosphere or an
ambient atmosphere of argon (Ar) or nitrogen (N.sub.2), thus filling the
space between the slit 64 and magnetic core 61 with glass filler 65 which
molds the magnetic core 61.
After molding the magnetic core in the above-mentioned manner, excess glass
filler is removed and the air-bearings 62a and 62b are subjected to a
finishing process to obtain the required depth of the magnetic gap to
complete a floating-type composite magnetic head.
When applying the finishing process to the air bearings, the magnetic gap
depth has thus been controlled by observing and measuring the apex using
an optical microscope and a micro-measurement scale, etc. installed to the
eyepiece section. When doing this, since the magnetic core is buried under
the glass filler for molding inside the slit as aforementioned it is
impossible to directly view the apex of the magnetic gap from the
direction perpendicular to the side surface of the magnetic core (for
example, the direction of arrow A in FIG. 6). Consequently, the apex is
measured by observing it from an inclined direction (for example, the
direction of arrow B in FIG. 6) across the glass filler by tilting the
magnetic head or the optical microscope.
Nevertheless, in the aforementioned method, since the focal distances to
different points along the ridge of the magnetic core differ and the image
of the edge line of the magnetic core appears indistinct owing to the
inclined observation, it becomes necessary to maintain a larger distance
between the objective lens and the magnetic head to obtain a clearer view
which in turn limits the task to highly skilled workers because of the
restriction to the use of higher magnification. Also, with the
aforementioned method wherein inclined measurement is carried out across
the glass filler, the measurement reading of the magnetic gap depth may be
smaller than the actual dimension owing to the fact that the refractive
index of glass is larger than that of air, and scratches applied to the
surface of the glass filler while processing the air bearings interfere
with the precise measurement of the apex point, thus making it extremely
difficult to initiate commercial mass production under high precision
control of the gap depth. Furthermore, when a housing made of ferrite is
employed, the dark coloring of the housing hinders a view of the gap
depth.
One possible solution to this problem is to provide a mark on the magnetic
core which can be used as a reference for the magnetic gap depth and to
measure the mark to determine the magnetic gap depth indirectly rather
than by performing direct measurement of the magnetic gap depth (in other
words, the apex position).
This method is already a known production method of thin-film magnetic
heads wherein, for example, a triangular-pattern mark 91 in FIG. 9 whose
width varies in the direction of the magnetic gap depth having one of its
apexes positioned level with the apex of the magnetic gap and a
rectangular-pattern mark 92 having one of its sides positioned level with
the apex of the magnetic gap are applied by a thin-film forming process.
When grinding the air bearing, the width of the triangular pattern x.sub.2
is measured and is then compensated on the basis of the measurement result
of the rectangular pattern width x.sub.4 thus making an indirect
measurement of the magnetic gap depth x.sub.3. (Refer to Japanese Patent
Laid-Open No. 49212/1990.)
Nevertheless, marks are applied by the thin-film forming process peculiar
to thin-film magnetic heads, whereas floating-type composite magnetic
heads which do not include the thin-film forming process in their
production, are not at all applicable to this method.
To solve this problem, Japanese Patent Laid-Open No. 121105/1990 suggests
measuring the magnetic gap depth using reference marks on a floating-type
composite magnetic head by a marking method entirely different from that
for the thin-film magnetic heads.
FIGS. 7 and 8 illustrate the said suggestion. To form the magnetic core
block 71 first, preparing a pair of ferrite wafers 73 and 74, their
contact planes 73a and 74a are mirror-finished. On said contact planes 73a
and 74a, preprocessing grooves 73b and 74b are provided at a fixed pitch
P. Further, on the contact plane 74a of the second wafer 74, a coil
winding clearance groove 72 is provided in the direction perpendicular to
the preprocessing grooves 74b, 74b . . . and on the contact plane 73a and
the opposite surface of the first wafer 73, a glass filler groove 76 and
notch groove 75 are provided respectively in the direction perpendicular
to the preprocessing grooves 73b, 73b, . . . . Subsequently, gap spacer
layers made of a material such as SiO.sub.2 are applied to respective
contact planes 73a and 74a by deposition before joining the contact planes
of first and second wafers 73 and 74. Then, glass rods 79, 78 and 77 are
inserted into the preprocessing grooves 73b and 74b, glass filler groove
76 and notch groove 75, respectively, before heating and melting said
glass rods to fix the first and second wafers 73 and 74 by molding the
preprocessing grooves 73b and 74b and the glass filler groove 76, and to
fill the notch groove 75 with glass filler.
The molded block thus formed is then cut along the dotted lines as given in
FIG. 7 and the cut-out blank is then kerf-machined to form the disc facing
part of track width t to complete the core block. The core block is
further sliced to form magnetic core 81 of the structure indicated in FIG.
8. Meanwhile, the magnetic gap 84 is formed along the contact planes of
the first and second wafers across the disc facing part.
Magnetic core 81 thus obtained is provided with a measuring mark 85 at a
prescribed position, corresponding to the apex, on its exposing external
side 83. After the core is inserted and cemented in the slit, indirect
measurement of the magnetic gap depth can be accomplished by measuring the
mark which can be viewed directly from outside.
In recent years, demands for high density storage have been increasing and,
simultaneously, the magnetic gap depth of floating-type composite magnetic
heads is becoming smaller and smaller thus requiring stricter dimensional
precision in relation to nominal dimensions.
Under such situation, with the aforementioned method whereby the mark is
machined onto the exposed external side of the core, issues hitherto
neglected are being highlighted, such as the positional accuracy of
machining being difficult to obtain because the distance between the apex
point and the mark is comparatively large, or only a slight incline of the
magnetic core cemented in the slit resulting in a serious error.
Furthermore, since the mark is made on the core block before slicing into
magnetic cores, it is comparatively difficult to place the mark at the
position which accurately corresponds to the apex with all the magnetic
cores thus produced owing to dislocation occurring when cemented, thus
making it necessary to measure the position of the apex and the mark with
each magnetic core before grinding the air bearings on the basis of the
respective measurement results. Therefore, it is necessary to classify
magnetic cores according to grinding amount, making mass-production
difficult.
SUMMARY OF THE INVENTION
The present invention intends to solve the problems with conventional
techniques and, concerning floating-type composite magnetic heads which
are constructed by molding a magnetic core inside the slit provided in the
air bearing using glass filler, intends to provide a floating-type
composite magnetic head equipped with at least one concave mark for
reading the magnetic gap depth on the side surface of the disc facing
plane of a magnetic core.
This invention also intends to provide a production method of a
floating-type composite magnetic head where the magnetic gap depth of the
magnetic core cemented in the slider slit can be precisely controlled.
This invention further intends to provide a floating-type composite
magnetic head where the influence of inclination of the magnetic core
cemented inside the slit can be substantially minimized.
To obtain the floating-type composite magnetic head of this invention, it
is necessary to use a magnetic head core having a concave mark at a
particular position relative to the apex position on the side surface.
Also, the floating-type composite magnetic head of this invention can be
produced by a production method wherein the concave mark is applied in
advance to the side surface of the magnetic core and said magnetic core is
inserted into a slit provided in the air bearing of the slider and molded
by glass filler before finish-machining the air bearings to control the
magnetic gap depth while observing the condition of said concave mark
appearing on the disc facing plane of the magnetic core.
The production method of this invention has the feature that finishing can
be carried out while observing the concave mark, provided on the side
surface of the magnetic core which is molded inside the slit provided in
the air bearing of the slider, from the direction perpendicular to the air
bearing. Also with this invention, either one or multiple marks can be
used to reference the apex when performing finish-machining while
observing said multiple concave marks to control the magnetic gap depth.
In this case, respective shapes, dimensions and relative locations of the
multiple marks are selected in accordance with the required level of
dimensional precision.
The concave marks can be applied by one of several well-known methods which
include ion-milling, machining, chemical etching and laser beam
processing. Of these methods, the laser beam marking method which does not
damage the magnetic core and is capable of high-precision mark application
can be suggested as a suitable method for the purpose of providing marks
under this invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a) and (b) are respectively a cross-sectional view and a side
elevational view indicating the relative positioning of concave marks and
the apex.
FIG. 2 is a drawing indicating the relative positioning of multiple concave
marks and the apex.
FIG. 3 shows a magnetic core provided with marks on its side surface.
FIG. 4 is all inclined view of an example of a magnetic core for use with
the floating-type composite magnetic head.
FIG. 5 is an inclined view of an example of a floating-type composite
magnetic head.
FIG. 6 is a drawing showing the status of a magnetic core molded inside the
slit by glass filler.
FIG. 7 is an inclined view indicating a block provided with the mark.
FIG. 8 is an inclined view indicating a conventional magnetic core provided
with a mark machined on the exposed external side surface of the core.
FIG. 9 is a drawing showing the positioning of measurement marks provided
on a thin-film magnetic head.
FIG. 10 is a drawing showing the structure of marking equipment.
FIG. 11 is a photograph depicting the texture of the side surface of a
ceramic magnetic core provided with marks.
FIG. 12 is a photograph depicting the texture of the upper surface of a
ceramic magnetic core provided with marks.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The exemplary embodiments shall now be referred to more particularly as
follows. This invention meanwhile shall not be limited to the exemplary
embodiments described below.
With all the embodiments given below, marks are applied by laser beam
processing, and the schematic drawing in FIG. 10 shows the structure of
the marking equipment used for said laser beam marking.
With this equipment, illumination light emitted from a microscope light
source 101 lights up workpiece 104 placed on a stage 103 through an
objective lens 102 and reflected light from the workpiece is guided into
image pickup equipment 105 consisting for example of a CCD camera
installed to the body tube of the microscope to display the image on a
monitor 106 so that the apex which represents the magnetic gap depth of
the magnetic core of workpiece 104 may be observed and its position may be
measured by means of an image processor (omitted from the drawing). The
irradiation position of the laser beam being emitted from laser beam
emitter 107 can be indicated for checking purposes on the monitor by the
effect of the guide light being emitted from guide light source 108
located coaxially with the optical axis of the laser beam.
When applying a concave mark on a magnetic core using this equipment, the
image of the magnetic gap area of the magnetic core is first displayed on
the monitor by means of the optical microscope system to measure the apex
position which represents the magnetic gap depth using the image
processor, before making adjustment so that the apex position and the
starting point of laser irradiation come to a prescribed correlation using
the guide light as the reference light, thus accurately setting the mark
position. Subsequently, a concave mark is subsequently formed at the
prescribed position by irradiating, for example, a pulse oscillating YAG
laser beam.
A characteristic feature of this laser beam marking equipment is that it is
capable of measuring the apex distance with each of multiple magnetic
cores aligned in the workpiece and of setting the marking position
accordingly before providing the mark by laser beam. By use of a mask to
prescribe the contour of the mark, it is also possible to apply a mark on
the magnetic core by a single shot. Since the mark thus formed is a
concave mark etched by laser beam on the side surface of the magnetic
core, the existence/nonexistence of the mark on the processing surface and
its dimensions etc., can be observed through an ordinary microscope midway
during the machining of the air bearings from the machining direction,
namely, the direction perpendicular to the air bearing.
(Embodiment 1)
To produce the magnetic core, a pair of C-shaped section and I-shaped
section blocks made of monocrystal ferrite were prepared, the contact
planes of which were mirror-finished before forming a gap spacer on the
planes constituting the magnetic gap. Subsequently, the two blocks were
joined together and molded using glass filler before slicing at prescribed
intervals to complete the magnetic cores.
The multiple magnetic cores thus obtained were aligned and fixed in the
marker jig (workpiece) and mounted to the laser beam marking equipment for
application of a mark of prescribed shape and dimensions before performing
step-machining to complete the magnetic cores for use with the
floating-type composite magnetic head.
FIG. 3 shows the structure of a magnetic core 31 thus produced wherein the
C-shaped core 32 and I-shaped core 33 are cemented together by glass
filler 38 and two marks 36 positioned to the prescribed correlation with
the apex 35 are provided on both sides across the magnetic gap 34. These
marks are of right-angled isosceles triangle shape in concave profile and
the apex of these marks of the shape are positioned level with the apex
point of the magnetic gap depth. The dimension of the two sides of the
right-angled isosceles triangle is 6 um and the concave depth is 1 um,
taking less than a second to form the marks by laser beam irradiation. The
distance 37 represents the magnetic gap depth under such condition.
The magnetic core thus provided with concave marks is cemented inside the
slit in the slider and excess glass is removed before finish-machining the
air bearings to control the magnetic gap depth.
When performing finish-machining of the air bearings, multiple composite
slider assemblies (CSA) adhered to a lapping jig are ground down to a
prescribed depth such as, for example, the virtual magnetic gap depth
(BGd)+20 um from the surface of the lapping jig. Subsequently, finishing
to a level of BGd+5 um is performed using a lapping machine while checking
the marks from above using a metallurgical microscope of a magnification
of .times.200 to .times.400.
FIGS. 1(a) and (b) are explanatory drawings of the status of the marks thus
provided wherein FIG 1(b) shows the side surface near the magnetic gap and
FIG. 1(a) is a cross-sectional view taken along the dotted line a--a in
FIG.1(b). As grinding of the cores 12 and 13 progresses, marks 16 which
initially could not be seen from the air bearing side become visible as
shown in FIG. 1(a) and the magnetic gap depth 18 can be determined by
measuring the width W.sub.1 of the marks. Therefore, these marks can be
observed and checked as necessary during the succeeding process of
polishing by lapping before concluding machining when prescribed
conditions are obtained. By this method, the magnetic gap depth is
controllable to a very high degree of precision and a floating-type
composite magnetic head of a stable quality is obtainable.
In this embodiment, marks of a triangular shape were adopted but the shapes
and dimensions of the mark and the positional correlation between the mark
and the apex can of course be selected optionally.
(Embodiment 2)
High permeability magnetic films were applied to the magnetic head facing
planes of both the blocks by the spattering method and the gap spacer was
provided after that. Following almost the same procedure as with
embodiment 1 for the rest of the processes, magnetic cores were produced
and 3 marks as shown in FIG. 2 were applied to each of them.
These marks are to be provided with, for example, the following
correlations. Mark "a" and mark "b" are positioned with a level difference
in the upper ends of 2 um while the lower ends remain level. Mark "c" is
lower at the upper end than mark "b" by 2 um and the level difference
between its lower end and the lower ends of marks "a" and "b" is 1.5 um.
The lower end of mark "b" is positioned at 3 um apart from the apex
position.
Before finish-machining the air bearings, the distance between the upper
ends of the magnetic cores (air bearing side of the slider) and the apex
position remains at about 50 um. Therefore, rough machining can be
performed until mark "b" appears at which time finish-machining should be
adopted until mark "b" completely disappears, thus providing
high-precision control of the magnetic gap depth.
A metallurgical microscope should be used to check the concave marks
periodically by observing the mark forming location near the gap between
the magnetic cores from above the air bearing. FIG. 11 is a microscopic
photograph of the applied marks and FIG. 12 is an observational photograph
of the status of marks which appeared on the disc facing plane of the
magnetic core during machining.
Different from embodiment 1, this embodiment features the advantage that
the magnetic gap depth can be determined by observing the number of
marking patterns appearing at prescribed distances from the magnetic gap
instead of measuring the size (dimension) of the mark appearing on the air
bearing side.
In this embodiment, an example involving the use of 3 marks was described,
but the number, shapes and correlations of the marks can be optionally
selected depending on required magnetic gap dimensions and precision, in
an embodiment of this invention.
With this invention, since the marks provided on the side surface of the
magnetic core can be directly measured from the direction perpendicular to
the air bearing, the influence of the refractive index of glass is minimal
and since there is no fear of interference between the objective lens of
the eyepiece and the magnetic head, measurement under a higher
magnification is available thus enabling high-precision control of the
magnetic gap depth. Furthermore, the influence of possible inclination of
the magnetic core cemented inside the slit is also minimal.
Embodiments of this invention shall not be limited to those exemplified in
the above, but various variations can be available within the range of the
claims.
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